Radioactivity: the spontaneous decay or disintegration of an unstable atomic nucleus, accompanied by the emission of ionizing radiation, generally alpha or beta particles, often accompanied by gamma rays from the nuclei of an unstable isotope.
Half-life: the time required for the activity of a given radioactive substance to decrease to half of its initial value due to radioactive decay. The half-life is a characteristic property of each radioactive species and is independent of its amount or condition. The effective half-life of a given isotope on the body is the time in which the quantity in the body will decrease to half as a result of both radioactive decay and biological elimination. Half-lives vary from millionths of a second to billions of years.
Ionizing radiation: any radiation that displaces electrons from atoms or molecules, thereby producing ions. Alpha, beta, and gamma radiation are examples. Ionizing radiation may damage skin and tissue.
Alpha particle (alpha radiation): a positively charged particle ejected spontaneously from the nuclei of some radioactive elements. It is identical to a helium nucleus that has a mass number of 4 and an electrostatic charge of plus 2. It has low penetrating power and short range. The most energetic alpha particle will generally fail to penetrate the skin. Alpha is hazardous when an alpha-emitting isotope is introduced into the body. Alpha particles are the least penetrating of the three common types ofradiation (alpha, beta, and gamma) and can be stopped by a piece of paper (cannot penetrate skin).
Beta particle (beta radiation): a charged particle emitted from a nucleus during radioactive decay, with a mass equal to 1/1827 that of a proton. A negatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron. Large amounts of beta radiation may cause skin burns, and beta emitters are harmful if they enter the body. Most beta particles can be stopped by aluminum foil.
Gamma rays (gamma radiation): the most penetrating of the three types of ionizing radiation, gamma rays are electromagnetic radiation like light, radio waves and microwaves. Similar to X-rays, but usually more powerful, they have no mass; they are only
energy. Gamma rays are best stopped or shielded against by dense material such as
concrete or lead.
Radiation sickness: the complex of symptoms characterizing the disease condition known as radiation injury, resulting from excessive exposure of the whole body (or a large part) to ionizing radiation.
Dosimetry: the measurement of radiation doses. It applies to both the devices used (dosimeters) and to the techniques.
Units for measurement of radioactivity:
- Roentgen (r): a unit of exposure of gamma (or X-ray) radiation in field dosimetry. One roentgen is essentially equal to one rad. A unit for measuring the amount of radiation energy imparted to a volume of air. The roentgen can be used only to measure X-rays or gamma rays.
- Becquerel (Bq): the basic unit to describe the intensity of radioactivity in a sample of material. One Bq is equal to one disintegration (nuclear transformations) per second. Several commonly used multiples of the Bq are given:
- kilobecquerel (kBq): thousand becquerels
- megabecquerel (MBq): million becquerels
- giga-becquerel (GBq): billion becquerels
- terabecquerel (TBq): trillion becquerels
- petabecquerel (PBq): quadrillion becquerels
- Curie (Ci): a basic unit to describe the intensity of radioactivity in a sample of material. One curie is equal to 37 billion disintegrations (nuclear transformations) per second, or 37 billion bequerels. So, in one curie, 37 billion atoms decay in one second. Several commonly used fractions of the curie include:
- millicurie (mCi): 1/1,000 Curie
- microcurie (μCi): 1/1,000,000 Curie
- nanocurie (nCi): 1/1,000,000,000 Curie
- picocurie (pCi): 1/1,000,000,000,000 Curie
Exposure rate: the amount of energy from gamma or x-ray radiation transferred in a standard volume of air [expressed in units of microRoentgen per hour (μR/hr), milliRoentgen per hour (mR/hr), Roentgen per hour (R/hr), etc.].
Units of radioactive dose measurement:
- Gray (Gy): the world standard unit of radiation dose or energy absorbed per unit tissue mass. One Gray is equal to 1 joule per kilogram or 100 rads.
- Roentgen equivalent man/mammal (rem): one rem is the quantity of ionizing radiation of any type which, when absorbed by man or other mammals, produces a physiological effect equivalent to that produced by the absorption of 1 roentgen of X-ray or gamma radiation.
- Sievert (Sv): the world standard unit of radiation dose, effective dose, and committed dose. One Sievert is equal to 100 rem, an older unit of measurement used to measure the biological effects of ionizing radiation.
Geiger-Mueller (G-M) detector: a radiation detector which is generally used to measure the gamma, or (beta + gamma) radiation depending on whether the detector is covered by a beta shield.
Film badge: a photographic film packet to be carried by personnel, usually in the form of a badge, used for measuring and permanently recording gamma ray dosage. A thermoluminescent dosimeter is a type of film badge.